Estimating purity of Cd, Zn, Pb by non-contact measurement of specific electrical resistance at liquid nitrogen temperature

Abstract

High-purity fusible metals Cd, Zn, Pb and archaeological archPb are used as component elements in semiconductor and low-background scintillation detectors based on CdTe, CdZnTe, CdWO4 PbWO4 , ZnWO4 required for registering ionizing radiation and searching for particles of dark matter, rare alpha and beta decays. The detection efficiency and the sensitivity of detectors significantly depend on the purity of the constituent elements of detector materials. The dependence of the resistivity of fusible metals Cd, Zn, Pb on the degree of their purity was studied using the non-destructive technique of registering the decaying vortex currents induced in cylindrical samples after dropping the external magnetic field. The aim of the work was to determine the possibility of evaluating the purity of fusible metals using a simple methodology for measuring the characteristic times of decay of vortex currents at 77 K without the use of liquid helium. The computer analysis of the recorded signals presented in the form of decaying curves allowed finding the areas where the signal can be represented as an exponent with a characteristic decay time τ and determining a formula that related τ, specific resistance ρ, and the diameter of cylindrical samples. A comparison of the ρ values of both the initial samples of cadmium, zinc, lead, and archaeological lead, and those samples after various purification procedures, allowed establishing the dependence of the resistivity on the purity of the studied materials at the temperature of liquid nitrogen ρ77. The greater the difference in the purity of the fusible metal, the more their values ρ77 were different. Thus, the authors substantiated the possibility of a qualitative assessment of the purity of metals using contactless measurement and comparison of ρ77 for samples obtained after growing and various deep purification procedures.